Driving device for a passenger restraint system

ABSTRACT

In a driving arrangement for belt tensioners, a working chamber (32) is formed in a housing being assembled of several parts (10, 16), as well as an accommodation space (20) for a gas generator capsule (22), said space being in fluid connection with said chamber. The gas generator capsule (22) is encased by a sleeve (24) which is inserted in sealing contact between said parts (10, 16) of the housing in its accommodation space (20). A pre-chamber (26) is formed in the sleeve (24) opposite the bottom of said gas generator capsule (22).

The invention relates to a driving arrangement for an occupant restraintsystem, in particular a belt tensioner, comprising a housing assembledof several parts, in which housing a working chamber is formed as wellas an accommodation space for a pyrotechnic propellant charge, theaccommodation space being in fluid communication with the workingchamber.

Driving arrangements of this kind are known to exist in numerousversions. Such systems are generally divided into rotary drive andlinear drive arrangements. In both versions, the housing generallyconsists of a main body and a cover plate placed on an open side of thismain body. In the case of a rotary drive, a rotor is arranged inside thehousing, which may be a vane-type rotor or a rotary piston rotor. In thecase of linear drives, the housing contains a cylinder with a pistonmovably arranged therein. The working chamber is formed in both casesbetween the joined housing parts. The generally cylindricalaccommodation space for a pyrotechnic gas generator capsule opens intothe working chamber. The housing parts are clamped against each other bymeans of a plurality of screws or rivets. On activation of thepropellant charge in the gas generator capsule, an extremely highpressure of short duration develops in the accommodation space of thehousing, which may reach a value of 400 to 500 bar or even more.

The invention proceeds from the understanding that immediately after theactivation of the gas generator leakage losses occur in theaccommodation space of the housing due to the high pressure, resultingin an uncontrolled compressed gas flow into the working chamber. Underthese conditions of high pressure stress, the screws or rivets lengthenand a gap is formed which allows further leakage losses. If apre-chamber is arranged between the accommodation space in the housingand the working chamber, it then becomes possible to dimension thepassage section leading into the working chamber in a suitable way, andso to influence the pressure versus time profile, and to adapt it to theconstructural parameters of the working piston. When the passage sectionleading into the working chamber is reduced, for a short time afteractivating the gas generator the pressure in the working chamber will beconsiderably lower than that in the pre-chamber. The high pressure inthe accommodation space and in the pre-chamber increases the tendency ofleakage losses occurring.

The invention effectively prevents the occurrence of leakage losses inthe region of the accommodation space and the pre-chamber, if provided.According to the invention, a sleeve surrounding the propellant chargeis provided, which sleeve is arranged as a seal between the parts of thehousing in its accommodation space. The sleeve forms a sealing along theinner surface of the accommodation space, especially at the partingjoint between the housing parts. The compressed gases released by thepropellant charge are conducted along the inner surface of the sleeve tothe working chamber. In the preferred application of the invention on arotary drive with a vane-type rotor, a surprisingly high power increasehas been noted. This is to lead back on the one hand to the avoidance ofleakage losses immediately after activation of the propellant charge,and on the other hand to the additional design possibilities madeavailable by the presence of the sleeve. The realisation that a gap maymaterialize between the two force-joined housing parts at the moment ofactivation, through which gap compressed gas escapes, is not to reach inthe light of conventional consideration or general investigations. Theentire driving process, from the activation of the gas generator to thebelt being tensioned, proceeds within a few milliseconds, making adetailed investigation of the leakage situation almost impossible. Ifthe sleeve is extended axially over the length of the gas generatorcapsule receiving the propellant charge, it may also be used forembodying a pre-chamber arranged upstream of the working chamber, inorder to influence the gas pressure versus time profile and to adapt itto the requirements of the driving arrangement.

Preferably, the materials and the wall thicknesses of the sleeve and ofthe gas generator capsule are of such a nature that the sealing contactbetween the sleeve and the inner surface of the accommodation space ison the one hand enhanced by the radial expansion pressure of thepropellant charge, when activated, and on the other hand by the supportprovided for the sleeve in the accommodation space of the housing. Atthe same time, the sleeve is pressed against the wall of theaccommodation space in the housing, thereby also increasing the sealingeffect in that area.

The components of the housing, i.e. a main body and a cover plate, arepreferably realized as shaped parts, for example light alloy die-castparts, in order to allow an efficient series fabrication. Theaccommodation space for the propellant charge is constituted by twooppositely arranged recesses in the main body and the cover plate,respectively. In order to facilitate the separation of the shaped partsfrom the mold, these recesses run out with an obtuse angle at theparting plane between the main body and the cover plate. The sleeve ispreferably configured with two ribs parallel to the axis, the ribsadjoining the parting plane between the main body and the cover plateand improving the sealing effect gained by the sleeve, in particular onemploying an appropriate synthetic material for the sleeve.

Further features and advantages of the invention will be apparent fromthe following description and the drawings to which reference is made.In the drawings:

FIG. 1 shows a top view of the main body of a housing of a drivingarrangement, with the cover being removed;

FIG. 2 shows a sectional view of the driving arrangement of FIG. 1 withthe cover in position;

FIG. 3 shows a partial section of one of the embodiments;

FIG. 4 shows an expanded perspective view of the embodiment shown inFIGS. 1 and 2;

FIG. 5 shows a schematic sectional view of an embodiment of the drivingarrangement with a piston/cylinder linear drive;

FIGS. 6, 7 and 8 show three variants of a sleeve enclosing a capsule;

FIG. 9 shows a cross-section of an embodiment with a housing consistingof shaped parts;

FIG. 10 shows a section along line X--X in FIG. 9;

FIG. 11 shows a perspective view of a sleeve with a gas generatorcapsule inserted therein;

FIG. 12 shows a variant with a propellant charge directly placed into asleeve;

FIG. 13 shows a unit consisting of a sleeve, a propellant, an igniterand an outlet nozzle.

The embodiment of a driving arrangement for a belt tensioner, as shownin FIGS. 1 to 4, refers to a rotary drive with a vane-type rotor. Thedriving arrangement comprises a housing in two parts, the main body 10of which having a flat bottom as well as a circumferential wallprotruding therefrom, the wall delimiting a rotor chamber 12 which inturn contains the vane-type rotor 14. The open side of the main body 10is closed by a cover plate 16. The cover plate 16 is tensioned to themain body 10 by means of a plurality of screw bolts or rivets 18. In themain body 10, one half of the cylindrical accommodation space 20 isrecessed, and in the cover plate 16 the other half of this accommodationspace 20 is recessed. In the accommodation space 20, a pyrotechnic gasgenerator capsule 22 is incorporated which is surrounded by acylindrical sleeve 24. This sleeve 24 is extended to protrude over theaxial end of the gas generator capsule 22 to form a pre-chamber 26there, which opens, via a narrowed portion 28 and a nozzle 30, into aworking chamber 32 disposed upstream of the rotor chamber 12.

The gas generator capsule 22 has a thin-walled cup-like part with anannular collar 22a at the exterior end, for axial fixing in acorresponding seat in the accommodation space 20. FIG. 1 shows anelectric connector plug 34 for connection to an electric igniter of thegas generator capsule 22. A mechanical activation by means of apercussion igniter is likewise possible.

When properly dimensioned and made of a suitable material, the sleeve 24can have a sufficient strength to withstand the expansion pressuregenerated by the gas generator capsule on its activation. It may,however, also be made of a relatively soft material, such as aluminium.To improve the sealing effect at its inner axial end, an O-ring seal 36is additionally provided which is placed in an annular groove on theouter circumference of the sleeve 24 and abuts against the inner surfaceof the accommodation space.

Details of the rotary drive have no bearing on the invention and are,therefore, not dealt with in this description.

As can be seen from FIG. 2, the axis of the cylindrical gas generatorcap 22 lies in the parting plane between the main body 10 and the coverplate 16. When the gas generator capsule 22 is activated, its bottompart is blown off, since the cylindrical side wall is supported by theinner surface of the accommodation space 20 via the sleeve 24. Anextremely high pressure of short duration reaching several hundred baris now produced in the pre-chamber 26. As a consequence of the radialcomponent of the expansion pressure, the wall of the gas generatorcapsule 22 is pressed against the inner surface of the sleeve 24, andthe latter against the inner surface of the accommodation space 20. Agood sealing is achieved between the two contacting surfaces, preventingany leakage as well as an uncontrolled flow of the compressed gas intothe working chamber 32. The gas pressure profile versus time may beinfluenced by the design of the pre-chamber 26 with its narrowed portion28 and the nozzle 30, in order to achieve the best possible drive power.

In the embodiment shown in FIG. 3, the axis of the gas generator capsule22 is parallel to, but spaced apart from the parting plane between themain body 10 and the housing cover 16. The housing cover 16 is providedwith integrally formed wall sections 16a and 16b, which contact thesleeve 24 at its periphery and engage corresponding recesses in the mainbody 10 with an interlocking fit. The wall sections 16a and 16brepresent an extra path for possible leakage flows, which henceencounter an increased flow resistance.

In the embodiment shown in FIG. 5, the driving arrangement is a lineartensioner with a cylinder 40 and a piston 42 movably arranged therein,the piston engaging a belt buckle 46 via a traction cable 44. Thecylinder 40 is attached at one end to a housing which, as in theembodiment described above, comprises a main body 10 and a cover plate(not shown). The main body 10, in the same way as in the embodimentdescribed above, accomodates a gas generator capsule 22 enclosed by asleeve and sealed within the housing by this sleeve. The sealing may beachieved in the same way as in the embodiment described above, so that arepetition of the description is omitted.

In the embodiment according to FIG. 6, the sleeve 24 has a relativelythin wall and is made of a material of low mecanical strength. In thearea of the pre-chamber 26, the sleeve 24 is supported by the innersurface of the accommodation space 20. It should be noted that thesleeve 24 may be made of plastics or may be realised as a thin-walledaluminium cup. When realizing any such embodiment, a greater number ofscrew bolts or rivets 18 may become necessary.

In the embodiment shown in FIG. 7, a sieve 50 is provided inside thepre-chamber 26, in order to prevent the ejection of solid particles fromthe pyrotechnic charge and, in this way, ensure its complete combustion.

In the embodiment shown in FIG. 8, the sleeve 24 is provided with a stopat the inner end of the gas generator capsule 22, which stop is formedby a surrounding annular shoulder 52 and serves for axially supportingthe peripheral bottom rim of the gas generator capsule 22.

In the embodiment shown in FIGS. 9 to 11, the main body 10 and the coverplate 16 are realized as shaped parts, in particular as light alloydie-cast parts. The accommodation space for the gas generator capsule 22and the sleeve 14 is constituted by two oppositely arranged recesses 20aand 20b in the main body 10 and the cover plate 16, respectively. Forfacilitating the separation of the shaped parts from the mold, therecesses 20a and 20b each run out with an obtuse angle in the partingplane T between the main body 10 and the cover plate 16. As the recess20a has a greater depth than the recess 20b, approximatelytriangle-shaped spaces as viewed in cross-section materialize at theparting plane T, for receiving sealing ribs 14a, 14b of the sleeve 14,the ribs being correspondingly formed and parallel to the axis. At itsend face facing away from the gas generator capsule 22, the sleeve isprovided with an annular groove 60 with a sealing ring 62 insertedtherein.

In the embodiment shown in FIG. 12, the propellant enclosed, ifrequired, by a casing is directly inserted in the sleeve 14. The outletnozzle is closed by a bursting bottom 66. On the opposite side of thepropellant charge 64, there is arranged an igniter 68 being carried by abase 70. The base 70 is fixed in a predefined rotary position in thesleeve 14 by means of latching means 72. Due to the non-symmetric shapeof the sleeve (FIG. 11), there results a definite rotary position of theelectric plug-in contacts at the base 70 relative to the housing. Inthis embodiment, the sleeve 14 together with the propellant charge 64and the igniter 68 can be realized as a pre-assembled component. Theinterior space of the sleeve 14 is hermetically sealed by the burstingbottom 66, so that the propellant charge is protected against influencesfrom outside.

Departing from the embodiment according to FIG. 12, the variant in FIG.13 shows the igniter 68 integrated in the body of the sleeve 14. Aplug-in base 74 is an integral part of the sleeve, too. For enabling theinsertion of the propellant charge 64 and the igniter 68, the sleeve 14is open at one axial end. After insertion of the propellant 64, theigniter 68 and a sieve plate 50, the sleeve 14 is closed by means of abottom plate 76 in which the outlet nozzle 30 is formed closed off bythe bursting bottom. This bottom plate 76 can be bonded or welded to thesleeve.

I claim:
 1. A driving arrangement for an occupant restraint systemcomprising:a housing assembled of several parts (10,16), in whichhousing a working chamber (32) is formed as well as an accommodationspace (20) for a pyrotechnic propellant charge (22), the accommodationspace being in fluid communication with the working chamber; and asleeve (24) surrounding the propellant charge and being inserted betweenthe parts (10, 16) of the housing in its accommodation space (20) to actas a seal, characterized in that the propellant charge (64) is insertedin the sleeve (24) itself, together with an igniter (68).
 2. The drivingarrangement according to claim 1, characterized in that the sleeve (24)and the igniter (68, 70) are provided with interlocking elements (72)for fixing the igniter in its position in the sleeve.
 3. The drivingarrangement according to claim 1, characterized in that opposite to thepropellant charge (64) a pre-chamber (26) is formed in the sleeve (24),the pre-chamber comprising on its end facing away from the propellantcharge an outlet nozzle (30) which is hermetically sealed by a burstingbase (66).
 4. A driving arrangement for an occupant restraint systemcomprising:a housing assembled of several parts (10,16), in whichhousing a working chamber (32) is formed as well as an accommodationspace (20) for a pyrotechnic propellant charge (22), the accommodationspace being in fluid communication with the working chamber; and asleeve (24) surrounding the propellant charge and being inserted betweenthe parts (10, 16) of the housing in its accommodation space (20) to actas a seal, characterized in that a pre-chamber (26) is formed in thesleeve (24) opposite to the propellant charge.
 5. The drivingarrangement according to claim 4, characterized in that the pre-chamber(26) is shaped as a nozzle (30) at its end facing the working chamber(32).
 6. The driving arrangement according to claim 5, characterized inthat a sieve (50) is inserted in the pre-chamber (26).
 7. A drivingarrangement for an occupant restraint system comprising:a housingassembled of several parts (10,16), in which housing a working chamber(32) is formed as well as an accommodation space (20) for a pyrotechnicpropellant charge (22), the accommodation space being in fluidcommunication with the working chamber; and a sleeve (24) surroundingthe propellant charge and being inserted between the parts (10, 16) ofthe housing in its accommodation space (20) to act as a seal,characterized in that the housing consists of a main body (10) and acover plate (16) placed on an open side of the main body along a partingplane, and that the accommodation space (20) is formed by spacesrecessed partly in the main body and partly in the cover plate.
 8. Thedriving arrangement according to claim 7, characterized in that the axisof the cylindrical propellant charge lies in the parting plane of themain body (10) and the cover plate (16).
 9. The driving arrangementaccording to claim 7, characterized in that the axis of the cylindricalpropellant charge lies spaced apart from and parallel to the partingplane of the main body (10) and the cover plate (16), and that the coverplate has projecting wall parts (16a, 16b) contacting the propellantcharge and engaging corresponding recesses in the main body (10) with aninterlocking fit.
 10. The driving arrangement according to claim 7,characterized by the main body (10) and the cover plate (16) beingconfigured as shaped parts and having recesses arranged opposite to eachother, said recesses constituting the accommodation space (20) andrunning out in the parting plane at an obtuse angle.
 11. The drivingarrangement according to claim 10, characterized in that the sleeve (24)comprises two sealing ribs arranged parallel to the axis, the ribsprojecting radially from the peripheral surface of the sleeve and beingformed at the transition from the parting plane to the recess of themain body (10).
 12. The driving arrangement according to claim 7,characterized in that the sleeve (24) comprises on its inner end face anannular groove for receiving a sealing ring.